Signaling System #7 Kamalasanan.PK 4/22/2017 MSC Ernakulam

Types of Signaling Signaling in Telecommunications Network Channel Associated Signaling (CAS) Common Channel Signaling (CCS) Signaling System Number (SS7) is a form of Common Channel Signaling. 4/22/2017 MSC Ernakulam

Common Channel Signaling Out of Band signaling Employs separate, dedicated path for signaling. Voice trunks are used only when a connection is established, not before. Faster Call Setup. Switch A B Voice Trunks Signaling Link 4/22/2017 MSC Ernakulam

Advantage of CCS over CAS Faster call setup No interference between signaling tones by network and frequency of human speech pattern. Greater Trunking Efficiency:- CCS has shorter call set up time that result in less call holding time, thereby reducing the traffic on the network. Information Transfer:- CCS allows the transfer of additional information along with the signaling traffic providing facilities such as caller identification and voice or data identification 4/22/2017 MSC Ernakulam

SS7 Principle Out of band Signaling Higher Signaling data rates (56Kbps & 64 Kbps) for LSL and 2Mbps for HSL Signaling traffic is bursty and of short duration, hence operates in connectionless mode using packet switching Variable length signal units with maximum size limitation Optimum use of bandwidth Reliability and flexibility 4/22/2017 MSC Ernakulam

Definition SS7 or Signaling System Number 7 is a set of protocols that describes a means of communication between telephone switches in public telephone networks. SS7 is a highly sophisticated and powerful form of Common Channel Signaling (CCS). The use of out-of-band signaling procedures offers considerable benefits over and above other signaling methodologies. SS7 is a layered system, in which each layer (level) contains a well-defined functionality, including the interface (functions and procedures). 4/22/2017 MSC Ernakulam

SS7 Networks STP 4/22/2017 MSC Ernakulam

Service switching point (SSP) SSPs are switches that have SS7 software and terminating signaling links SSPs create packets (signal units) and send those messages to other SSPs, as well as queries to remote shared databases to find out how to route calls SSPs communicate with the voice switch via the use of primitives and have the ability to send messages using ISUP (call setup and teardown) and TCAP (database lookup) protocols. The switch can originate, terminate, or switch calls 4/22/2017 MSC Ernakulam

Signaling transfer point (STP) STPs are packet switches, and act like routers in the SS7 network. Routes each incoming message to an outgoing signaling link, based on routing information contained in the SS#7 message and a pre-defined route table Does not offer termination services STPs are paired to ensure redundancy 4/22/2017 MSC Ernakulam

Service control point (SCP) An SCP is usually a computer used as a front end to a database system. It is an interface to application-specific databases. The address of an SCP is a point code, and the address of the database it interfaces with is a subsystem number. The database is an application entity which is accessed via the TCAP protocol. Databases that provides information necessary for advanced call processing capabilities Accepts a query for information from a subsystem at another node 4/22/2017 MSC Ernakulam

SS7 Link Types STP STP STP STP STP STP STP STP 4/22/2017 MSC Ernakulam

SS7 Link Types A link (access) Connects signaling end point (SCP or SSP) to STP. B link (bridge) Join mated STP pairs to other mated STP pairs of equal hierarchy and forms a quad structure. C link (cross) Connects STPs performing identical functions, forming a mated pair (for greater reliability). Provide alternate routing. D link (diagonal) Connects local and regional STP pairs.One level of STP pairs ,the secondary or local level,supports SSPs. E link (extended) Connects an CSP,SSP or signaling point to a remote STP pair to perform transaction services. (Note: E links are not recommended) F link (fully associated) Connects SCPs,SSPs and signaling points directly with one another.F links donot connect to STPs 4/22/2017 MSC Ernakulam

Common Channel Signaling Modes There are three types of CCS signaling modes: Associated Quasi-associated Non-associated SS7 runs in associated or quasi-associated mode, but not in non-associated mode. Associated and quasi-associated signaling modes ensure sequential delivery, while non-associated does not. SS7 does not run in non-associated mode because it does not have procedures for reordering out-of-sequence messages.

Associated Signaling both the signaling and the corresponding user traffic take the same route through the network. Associated mode requires every network switch to have signaling links to every other interconnected switch (this is known as a fully meshed network design).

Quasi-Associated Signaling In quasi-associated mode, signaling follows a different route than the switched traffic to which it refers, requiring the signaling to traverse at least one intermediate node. Quasi-associated networks tend to make better use of the signaling links.

LINK LINKSET PC = 1 PC = 2 ROUTE NODE A NODE B ROUTSET NODE C PC = 3 4/22/2017 MSC Ernakulam

LINK – Physical channel used for signaling. LSL (Low Speed Link )- having a speed of 64Kbps HSL (High Speed Link) – Having a speed of 2Mbps LINKSET – Group of links between two nodes. For LSL max of 16 links can be in a Linkset For HSL max of 4 links can be in a Linkset LINKSET GROUP – Group of Linkset in which priority has been given ROUTE – Logical path between two nodes utilizing the linkset . ROUTESET – Group of Routes two a specific destination. 4/22/2017 MSC Ernakulam

What goes over Signaling Link Signaling information is passed over the signaling link in form of messages, which are called signaling units (SUs) 3 Types of SUs are: Message signal units(MSUs) Link status signal units(LSSUs) Fill-in signal units(FISUs) 4/22/2017 MSC Ernakulam

Message signal unit (MSU) Signaling Units Message signal unit (MSU) Carries signaling associated with call setup & database query and response and SS7 network input 1 1 1 1 1 8-272 1 FLAG BSN/ BIB FSN/ FIB Length Indicator Service Info. octet Signaling Info. field Check sum 4/22/2017 MSC Ernakulam

Signaling Units FLAG: Beginning of a new SU and is 01111110 BSN: Used to acknowledge receipt of SUs BIB: Indicate the negative acknowledgement by the remote SP when toggled FSN: Sequence number of the SU FIB: Used in error recovery like BIB SIO: Service Information Octet SIF: Signaling Information Field CRC: Cyclic Redundancy check 4/22/2017 MSC Ernakulam

Direction of transmission Signaling Units Passing in Physical Layer Format of Message Signal Unit (MSU) F CK SIF SIO S P A R E LI F I B FSN B I BSN F Direction of transmission Format of Link Status Signal Unit (LSSU) F CK SF S P A R E LI F I B FSN B I BSN F Format of Fill-in Signal Unit (FISU) F CK S P A R E LI F I B FSN B I BSN F F – Flag (8) SIF – Signaling Information Field (8n, n>2) CK – Checksum (16) SIO – Service Information Octet (8) LI – Length Indicator (6) FIB – Forward Indicator Bit (1) FSN – Forward Sequence Number (7) BIB – Backward Indicator Bit (1) BSN – Backward Sequence Number (7) SF – Status Field (8 or 16) 4/22/2017 MSC Ernakulam

LENGTH INDICATOR · LI = 0 indicates a FISU. LI = 1 or 2 indicates an LSSU. LI > 2 indicates a MSU 4/22/2017 MSC Ernakulam

Link status signaling units (LSSU) Inform the far end about the changes in status of link Message length can be 1 or 2 bytes FLAG BSN/ BIB FSN/ FIB Length Indicator Check Sum 1 Status Field 1 or 2 4/22/2017 MSC Ernakulam

Network Management (LSSU) FORMAT.. USAGE OF CBA 4/22/2017 MSC Ernakulam

Fill-In Signal Units (FISU) Signaling Units Fill-In Signal Units (FISU) Fill the gaps between MSU and LSSU messages Sent only when the buffer is empty, to keep the signaling link active Facilitate in constant monitoring of link quality. FLAG BSN/ BIB FSN/ FIB Length Indicator Check Sum 1 4/22/2017 MSC Ernakulam

Message Signaling Unit F S P A R E SIF B I LI CK BSN FSN SIO 8 7 1 6 2 2-272 Bytes 16 01111110 279 Bytes Q:How many MSU’s with fully loaded SIF’s will tranfer in One second? Total Time required to transmit 1 MSU with 272 bytes SIF 1 bytes = 125 Micro second One MSU = 279 X .000125 = 0.0348 Seconds 1 Second = 28 MSU’s 4/22/2017 MSC Ernakulam

SS7 Protocol Stack OSI SS7 4/22/2017 MSC Ernakulam

Protocols Message Transfer Part (MTP Level 1) Physical Provides an interface to the actual physical channel over which communication takes place CCITT recommends 64Kbps transmission as LSL whereas ANSI recommends 56 Kbps HSL provides a transmission speed of 2Mbps 4/22/2017 MSC Ernakulam

SS7 Protocol Overview The SS7 physical layer is called MTP level 1 (MTP1) The data link layer is called MTP level 2 (MTP2), The network layer is called MTP level 3 (MTP3). Collectively they are called the Message Transfer Part (MTP). The MTP transfers the signaling message, in the correct sequence, without loss or duplication. The MTP provides reliable transfer and delivery of signaling messages.

MTP2 MTP2 ensures reliable transfer of signaling messages. It encapsulates signaling messages into variable-length SS7 packets. SS7 packets are called signal units (SUs). MTP2 provides delineation of SUs, alignment of SUs, signaling link error monitoring, error correction by retransmission, and flow control. The MTP2 protocol is specific to narrowband links (56 or 64 kbps).

MTP3 MTP3 performs two functions: Signaling Message Handling (SMH) Delivers incoming messages to their intended User Part and routes outgoing messages toward their destination. MTP3 uses the PC to identify the correct node for message delivery. Each message has both an Origination Point Code (OPC) and a DPC. The OPC is inserted into messages at the MTP3 level to identify the SP that originated the message. The DPC is inserted to identify the address of the destination SP. Routing tables within an SS7 node are used to route messages. Signaling Network Management (SNM): Monitors linksets and routesets, providing status to network nodes so that traffic can be rerouted when necessary. SNM also provides procedures to take corrective action when failures occur, providing a self-healing mechanism for the SS7 network.

SCCP SCCP provides a more flexible means of routing and provides mechanisms to transfer data over the SS7 network. Such additional features are used to support non circuit-related signaling, which is mostly used to interact with databases (SCPs). It is also used to connect the radio related components in cellular networks and for inter-SSP communication supporting CLASS services. For example, in cellular networks, SCCP transfers queries and responses between the Visitor Location Register (VLR) and Home Location Register (HLR) databases.

Format of SCCP message. - - > F CK SIF SIO LI FIB FSN BIB BSN F Message Signal Unit 1st Bit Transmitted - - > F CK SIF SIO LI FIB FSN BIB BSN F SCCP Message Message Type MTP Routing Label SCCP Information Mandatory Variable Part Mandatory Fixed Part SLS OPC DPC Optional Part 4/22/2017 MSC Ernakulam

Protocols Transaction Capabilities Applications Part (TCAP) To establish more then one transaction between two ss7 nodes Exchange of non-circuit related data Between applications across the SS#7 network Using the SCCP service Queries and responses sent between Signaling Switching Point (SSPs) and Signaling Control Point (SCPs) Sends and receives database information Credit card validation Routing information 4/22/2017 MSC Ernakulam

Transaction Portion Package Types End Ends a dialog between two nodes Abort Terminates the dialog abruptly without transmitting any pending component Continue Continues the dialog (for example, more messages can be sent) Begin Starts a dialog between two nodes 4/22/2017 MSC Ernakulam

Basic ERROR CORRECTION -With Error 4/22/2017 MSC Ernakulam

Service Information Octet (SIO) In message signal units (MSUs), the service information octet (SIO) is used to perform message distribution. This octet is divided into a four-bit service indicator (SI) and a four-bit subservice field. This subservice field is further divided into a two-bit network-indicator code and two bits that are spare if the indicator code is 00 or 01, or are available for national use if the indicator code is 10 or 11. 4/22/2017 MSC Ernakulam

Sub-service field (4 bits) Service indicator (4 bits) SIGNALLING NETWORK FUNCTIONS Signaling Message Handling – SERVICE INFORMATION OCTET D C B A Sub-service field (4 bits) Service indicator (4 bits) Direction of transmission Sub-service field = Network Indicator (Bits A & B are spare) Bit D Bit C Network Indicator 1 International Network Not used National network Reserved for national use 4/22/2017 MSC Ernakulam

THANK YOU Kamalasanan 4/22/2017 MSC Ernakulam